Purely by coincidence, I had a conversation with an employee (I'll call him "Joe" for convenience) in a Kroger subsidiary early last week, after I had seen several customers in the store without masks, despite the signs at the entrance saying that masks are required by local ordinance.
Joe told me that Kroger says that no one except a store manager is allowed to confront* a customer about not wearing a mask — nor about shoplifting. In fact, Joe says, an employee can be fired for violating this rule.
I am guessing the rule may be intended to protect both Kroger and the employee, for liability and physical safety reasons.
* "Confront" here means verbally by mentioning the action, or physically even by obstructing the customer (or thief) from leaving.